Wave-signal responder system



Oct. 3, 1950 WOOD ETAL 2,524,492

WAVE-SIGNAL RESPONDER SYSTEM Filed July 22, 1947 ouNcH OSCILLATOR INVENTORS HUBERT WOOD FREDERIG C. WILLIAMS BY "JAMES R.WHITEHEAD Patented Oct. 3, 1950 UNITED srArs 2,524,492 WAVE-SIGNAL RESPONDER SYSTEM Hubert Wood, Hollinwood, Frederic C. Williams, Manchester, and James Rennie Whitehead, London, England, assignors to Ferranti Limited, Hollinwood, England, a corporation of Great Britain Application July 22, 1947, Serial No. 762,731 In Great Britain November 5, 1945 Section 1, Public Law 690, Aiigust s, 1946 Patent expires November 5, 1965 This invention relates to apparatus for use in wireless signaling systems of the kind in which a transmitter having a receiver associated therewith, is arranged to radiate a response signal in reply to an interrogation signal received by the associated receiver.

More particularly, the invention relates to such receiver-transmitter devices, usually known as responders of the type adapted for use with a pulsed interrogating signal and is an improvement in or a modification of the responder described and claimed in an application of Hubert Wood, Frederic C. Williams, and James R. Whitehead, Serial No. 29,288/45, filed in Great Britain on November 5, 1945, entitled Improvements Relating to Radio Receivers of the Type Associated with Transmitting Means, and assigned to the same assignee as the present appli cation.

For efiicient re-transmission in such a responder, hereinafter referred to as a responder of the type stated, a high driving power should be applied to the transmitting valve. In order to achieve this, it has been proposed in a copending application of Maurice K. Taylor et al., Serial NO. 762,642, filed July 22, 1947, entitled Wave- Signal Responder System, and assigned to the 5 Claims. (Cl. 250-15) f tateeither the provision of a resistance between the positive terminal of the high-tension supply same assignee as the present application, to em v ploy a cathode-follower stage for applying the receiver output as a driving potential to the transmitting valve.

A difiiculty frequently encountered with a responder either with or without the cathode-follower stage, lies in its ability to transmit signals derived from interference, say for example, from engine ignition pulses, besides those signals received from the remote interrogating station. These spurious signals, when received at the remote e. g. ground station, are confusing and they decrease the capacit of the system as a whole to handle wanted signals. Accordingly, it is advisa-ble to suppress the transmission of such spurious signals by preventing the interfering signals which initiate them from being applied to the transmitting valve.

When a responder of the type stated is provided with a cathode-follower stage, the suppression of the transmission of spurious signals may and hence do not cause the transmission of spuriousresponse signals.

In the arrangement described in the previous paragraph the manner of applying the negative grid bias potential "to the cathode-follower valve is usu'ally by the connection of a resistance between thejpositive terminal of the 'high tension supply, and the cathode of the cathode-follower valve whereby thepotential drop across the load resistance provides the requisite bias 'voltage.- The use of 1 such a 'resistan'cehas twodisadvantages. Firstly;-'sincethe resistance is, in effect, in parallel with. the high-tension supply, "the power consumption is large. Further; since the cathode of the cathode-follower valve is made more positive, the control grid of thetransmitting valve also becomes more positive because of the D; 0. connection which is usually provided thereto from the cathode of the cathode-follower valve. Hencein-order to obtain an appropriate negativebias potential on the control grid of the transmitting valve, its-cathode potential must also be made more. positive. This would necessiand the cathode of the transmitting valve or alternatively an increase in the. value, of the bias resistance .in the cathode lead of such valve.

The former method would increase still further the H. T. power consum tion whereas the latter method would havethe effect ofgreducing the upperlimit of the recurrence frequency of the interrogating pulses to which the apparatus of be eifected by arranging that the negative bias potential of the control grid with respect to the cathode of the cathode-follower valve exceeds that of the cutoff value by an amount which is greater than the potential amplitude of manybf the interfering signals. In consequence these signals are not applied to the transmitting valve the type stated would satisfactorily respond since I the number of signals per second with which the transmittingvalve' can deal determines the time constant of the cathode-grid circuit of the valve, i. e. is governed in part'by the value of the resistance between the cathode of the transmitting valve and the negative pole of the high-tension supply and the value of the condenser connected across that resistance.

cathode-follower stage, without; introducing the I above mentioned diflicultiess.

The value of the latter condenser, is, however, also a factor in determining thewidth of the pulse to be re-transmitted.

1 It is, therefore, necessary to choose a, value of the resistance which is small'enough to ensure that the condenser discharges between successive. sig-" Broadly, the invention resides in preventing the transmission of spurious signals by suitable biasing beyond the cutoff point of the transmitting valve instead of the cathode-follower valve as hitherto. This allows the latter valve to be operated normally with a control grid-to-cathode potential well above the cutoff point with the result that the positive potential of its cathode, which potential is transferred to the control grid of the transmitting valve, is appreciably lowered and in direct consequence, the positive potential which must be applied to the cathode of the transmitting valve in order to provide the requisite bias potential is similarly reduced. Such reduction of potential permits the use, if necessary, of a smaller value resistance with consequent improvement of the response to high pulserecurrence frequencies or the avoidance of wasteful resistance networks across the high-tension supply source, or both.

According to one form of the present invention, a wave-signal responder system comprises a wave-signal receiver for receiving an interrogating pulse-modulated wave signal and for deriving the pulse-modulation components thereof to provide a control signal of pulse wave form. The system includes a wave-signal transmitter including a transmitting valve, and. a cathode-follower stage for amplifying said control signal to provide a driving potential, the cathode-follower stage including a cathode load resistor conductively coupled to the control grid of the transmitting valve to apply thereto the driving potential and being normally biased to anode-current cutoff by a control grid-to-cathode bias voltage. The system also includes a high-tension voltage supply for energizing the valves thereof and a parallel resistor-condenser network connected between the negative terminal of the hightension su ply for energizing the tubes of the system and a common negative high-tension return lead to the transmitting tube and to at least one other tube in the system other than the tube of the cathode-follower stage. The cathode of the cathode-follower stage is connected by means of its load resistance directly to the negative hightension supply terminal.

The invention will now be described b way of example with reference to the accompanying drawing which shows the circuit arrangement of a responder of the type stated embodying the present invention.

This responder includes a superregenerative receiving stage comprising a superregeneratively operated valve I, the anode l6 of which is coupled to its control grid I2 by way of a tuned circuit, including inductance 6 and variable condenser 6a, and condenser I3. Inductance 6 is coupled by way of aerial coil 5 to an aerial, not shown. The variable condenser 6a is arranged to sweep cyclically through a chosen capacity range so as to vary the resonant frequency of the tuned circuit 6, So over a chosenfrequency band. The centre point 6' of coil 6 is joined to the positive terminal of a high-tension supply, the negative terminal of which is connected to a common return lead 1' by way of a resistance 48 in parallel with condenser 49. The cathode 2 of valve I is connected to common return 1' by Way of an auto-- biasing arrangement formed by resistance 3 and decoupling condenser 4. Control grid I2 is connected to common return 1' by a grid-leak resistance 9 while a quench-frequency oscillator is connected between the control grid I2 and common 4 return 1' for feeding quenching oscillations into the control grid cathode circuit of the valve I.

Anode I6 is also joined by way of condenser 20 to the anode 2I of a diode rectifier valve 22 whose cathode 23 is connected to common return 1'. A load resistance 24 is connected across this diode valve. Anode 2I is joined by way of a high-frequency choke 25 to the control grid 26 of a pentode amplifier valve 21, the suppressor and screen grids of which are connected in the normal manner. Anode 36 of valve 21 is joined by way of a load resistance 3| to the positive terminal of the high-tension supply while the cathode of this valve is connected to common return 1 by way of an auto-biasing network 28, 29.

A further connection is made from anode 36 by way of condenser 32 to control grid 33 of a cathode-follower valve 34 whose anode 35 is joined directly to the positive terminal of the high-tension supply and whose cathode 36 is connected by way of cathode load resistance 31 directly to the negative terminal of the high-tension supply. Control grid 33 is also connected to the negative pole of the high-tension supply by way of gridleak resistance 55. This cathode-follower valve is arranged to operate normally with a control grid-to-cathod bias potential well above the cutoff point.

Cathode 36 is joined by way of a direct-current path including a pulse-widening circuit comprising a condenser 39 and a parallel resistance II, and a high-frequency choke 40 to the control grid M of a triode transmitting valve I5, this control grid also being joined by way of a condenser I3' to the tuned circuit '6, 6a and condenser I3. The anode I6 and the cathode I1 0f triode valve I5 are respectively joined to anode I6 of triode valve I and to common return I.

In operation, when an interrogating signal pulse is received from a remote station it is amplified superregeneratively by valve I, rectified by diode valve 22 and the rectified output across load resistance 24 is then applied to pentode valve 21, the amplified output of this valve being then fed by way of cathode-follower valve 34 as a positive unidirectional potential to control grid I4 of valve I5. Control grid I4, which is normally biased to beyond cutofi in a manner to be described, thus becomes more positive whereby valve I5 commences to oscillate and effects transmission by way of the aerial coil 5. Valve I5 continues to oscillate until such timeas the grid current in the control grid circuit builds up an opposing potential across condenser 39 of sufficient amount to overcome the positive drive from valve 34 and to cause stoppage of oscillation in the known grid-squegging manner. During this period an output pulse is transmitted from the aerial in response to the interrogating pulse which initiated the operation of valve I5, the duration or width of this response pulse being determinedby the time constant of the grid cathode circuit of valve I5 and principally by the valve of condenser 39 and resistance 4|.

Due to its direct-current connection to the cathode 36 of valve 34, the control grid I4 of transmitting valve I5 is at a positive potential with respect to the negative high-tension supply terminal by the value of the potential drop across the load resistance 31. In order to bias the transmitting valve I5 beyond the cutoff point, the cathode I1 thereof must be made positive with respect to the negative high-tension supply terminal by an amountequal to the sum' Oi the potential drop across'load resistance 31,

the requisite bias potential for cutting off the said valve 15 and the chosen potential amplitude below which the re-transmission of response signals is reoulred to be avoided. The biasing of the cathode I7 is eilected by means of the resistance 48 in the H. T. negative supply to valves 1, l5 and. 27.

Since resistance 48 carries the total space currents of valves 1, l5 and 27, the necessary potential drop for adequate biasing voltage may be obtained across a resistance of relatively small value. This in turn allows condenser 49 although of adequately large capacity, to discharge in the interval between successive pulses. This desirable result is obtained without the need of any resistance paths in parallel with the high-tension supply and so avoids excessive power consumption. Furthermore, the cathode of the transmitting valve l5 may be directly connected to common return 7', i. e. without the usual series bias resistor arrangement and its parallel condenser.

The circuit formed by resistances 3 and condenser 5 which provides the grid-bias potential for valve I is arranged to have a very small time constant by making the value of condenser 4 small. This is possible since valve 2 has no high power drive applied to its control grid and does not transmit any powerful signals. Consequently, during the period when valve I5 is transmitting, the cathode current of valve I is small and condenser 4 is not charged to a high potential and in any event, it discharges very quickly through resistance 3.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A wave-signal responder system comprising, a wave-signal receiver for receiving an interrogating pulse-modulated wave signal and for deriving the pulse-modulation components thereof to provide a control signal of pulse wave form, a wave-signal transmitter includin a transmitting valve, a cathode-follower stage for amplifyin; said control signal to provide a driving potential, said cathode-follower stage including a cathode load resistor conductively coupled to the control grid of said transmitting valve to apply thereto said driving potential and being normally biased to anode-current cutoff by a control gridto-cathode bias voltage, a high-tension voltage supply for energizin the valves of said system, and a parallel resistor-condenser network connected between the negative terminal of the hightension supply for energizing the tubes of the system and a common negative high-tension return lead to the transmitting tube and to at least one other tube in said system other than the tube of said cathode-follower stage, the cathode of said last-mentioned tube being connected by way of its load resistance directly to said nega-' tive high-tension supply terminal.

2. A wave-signal responder system as claimed ting valve is connected directly to oneend of said resistor-condenser network. Y 1 e y 4. A Wave-signal responder system-as claimed in claim 1 in which the cathode of the valvein' said cathode-follower stage is conductively coupled to said transmitting valve through means for modifying the width of the pulses of said control signal translated by said cathode-follower stage. i

5. A wave-signal responder system as claimed in claim 4 in which said width-modifying means comprises a parallel-connected resistor-condenser network.

HUBERT WOOD.

FREDERIC C. WILLIAMS.

JAMES REN NIE WHI'IEI-IEAD.

REFERENCE S CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date: r 2,414,992 Wheeler Jan. 28, 1947 2,415,667 Wheeler Feb. 11, 1947 2,429,513 Hansen et a1. Oct. 21, 1947 2,432,033 Nicholson, Jr. Dec. 2, 1947 1 pass through I 

